1. Field of the Invention
The present invention relates to a wideband acoustic echo cancellation apparatus with an adaptive tail length in an embedded system, and a wideband acoustic echo cancellation method, and more particular, to a technology of cancelling an acoustic echo that is input to a microphone via various paths and transferred to a far-positioned speaker.
2. Description of the Related Art
An acoustic echo may arise when a sound signal output through a speaker in a terminal is input to a microphone via various paths and is transferred to a far-positioned speaker. An acoustic echo cancellation apparatus refers to an apparatus for cancelling the acoustic echo.
To cancel the acoustic echo, various methods using time space and frequency space may be used. The various methods have been improved to satisfy criteria, for example a convergence time to lower the acoustic echo below a predetermined level, a long echo path processing ability, a simultaneous call detection time, a calculation amount, and the like.
In general, a long echo path, namely one of performance indexes of the acoustic echo, may be used as a criterion for estimating an echo environment coefficient by storing an input signal in a memory for a long time period M.
A number of taps of an adaptive filter may also be operated based on the time period M. The adaptive filter may mainly perform filtering of an adaptive filter coefficient that may be defined to be an echo similar to a reference far-end signal, may perform calculation of a difference between a near-end signal and similar echoes that may be defined to be errors, and may perform updating of the adaptive filter coefficient.
The above operations may be performed by arithmetic operations, such as multiplication and addition. Accordingly, as a number of coefficients increases, a processing apparatus with a higher performance may be required. Therefore, a large number of researches have been conducted to reduce a number of coefficients of a filter.
To remove the acoustic echo using the adaptive filter, an energy of an input far-end signal may be calculated, a far-end signal set used as a criterion may be multiplied by a current adaptive filter coefficient set, addition (filtering) may be performed, and a similar echo value may be obtained. As a result of subtracting similar echo signals from the near-end signal, that is, an operation of dividing an error value by a far-end signal energy, of multiplying a far-end signal set, of multiplying a filter step coefficient ‘mu’, of adding a previous adaptive filter coefficient value, and of updating a coefficient value of the adaptive filter may be repeatedly performed.
A length of a tail that is generally required in a typical acoustic echo cancellation apparatus may be 128 milliseconds (msec), and may be converted to a number of samples, namely, 2048 samples obtained by ‘128*10−3*wideband sampling frequency (16 KHz)’.
In other words, the time period M may have a value of ‘2048’. However, complexity of an operation of the adaptive filter may further increase, as the value of the time period M increases.